Molding method of sand mold using foamed sand, molding die, and sand mold

ABSTRACT

A molding method of a sand mold including a hardened layer in a predetermined thickness range from an outer layer part, includes: forming a cavity and a filling opening of a die so that a dimension, which is a largest dimension between two intersections of straight lines passing through a section of a boundary portion between the cavity and the filling opening of the die, with respect to an outside line of the section, is less than a predetermined ratio with respect to a thickness dimension of that part of a product portion of the sand mold from which a blowing opening molded in the filling opening projects, the product portion being formed by the cavity of the die; and filling foamed sand into the cavity from the filling opening of the die.

This is a Divisional of application Ser. No. 15/029,116 filed Apr. 13,2016, which is a National Stage Application of PCT/IB2014/002111 filedOct. 15, 2014. The entire disclosures of the prior applications arehereby incorporated by reference herein their entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a sand mold using foamed sand, amolding method of a sand mold, and a molding die for a sand mold.

2. Description of Related Art

On molding a product having a hollow portion, a collapsible sand core isused. As a molding method of a sand core, a technique using foamed sandobtained such that binder containing water glass is stirred with anaggregate so as to be foamed has been developed (for example, JapanesePatent Application Publication No. 2013-169582 (JP 2013-169582 A),Japanese Patent Application Publication No. 2013-111602 (JP 2013-111602A)). In the technique, a sand-mold molding device 1 illustrated in FIG.3 is used. The sand-mold molding device 1 is to mold a sand core (sandmold) for aluminum casting, for example, by hardening foamed sand S, andincludes a die 2 having a cavity C for molding the sand core, and afilling device 3 for filling the foamed sand S into the cavity C of thedie 2.

The die 2 is to form the cavity C by clamping an upper die and a lowerdie. The die 2 is provided with a filling opening 5 for communicatingthe cavity C with a sand tank 12 of the filling device 3. The fillingdevice 3 includes a sand tank 12 for mixing and accumulating the foamedsand S and pressurization mechanism (pressurizing means) 13 forpressurizing the foamed sand S in the sand tank 12. Then, the die 2 isset in the sand tank 12, and the foamed sand S in the sand tank 12 ispressurized by the pressurization mechanism 13, so that the foamed sandS is filled into the cavity C of the die 2 via the filling opening 5.The die 2 is heated to around 150° C. to 300° C., so as to vaporizewater in the foamed sand S filled in the cavity C, thereby solidifyingthe foamed sand S. After that, the die 2 is opened and a sand coremolded hereby is taken out therefrom.

As described above, when the foamed sand S is filled into the cavity Cof the die 2 so as to perform molding, an internal pressure of thecavity C of the die 2 is increased due to evaporation of water andthermal expansion of air bubble in a heating and hardening process ofthe foamed sand S. Hereby, water glass and an aggregate are accumulatedin an outer layer part of a molded product, so that a minute hardenedlayer having a necessary strength is formed in a predetermined thicknessrange from the outer layer part of the molded product. As a result, avulnerable portion that is fragile due to a low density is formed insidethe molded product. Further, when the density is markedly unbalanced,the vulnerable portion may become hollow. When the sand core is used forcasting, the strength required for the sand core is secured by thehardened layer, and the vulnerable portion or hollow portion contributesto collapsibility after the casting, thereby making it possible to takeout the core from a casting product.

SUMMARY OF THE INVENTION

In the meantime, when the foamed sand S is filled into the cavity C ofthe die 2 so as to perform molding, the filling opening 5 for sendingthe foamed sand S into the cavity C is also filled with the foamed sandS, and the foamed sand S in the filling opening 5 is also heated andhardened. Accordingly, a hardened layer is formed in a predeterminedthickness range from an outer layer part of the foamed sand S (a blowingopening) thus hardened in the filling opening 5, and a vulnerableportion or hollow portion is formed thereinside. The blowing opening isintegrated with a product portion, and is removed at the time ofcasting. However, if the vulnerable portion or hollow portion of theblowing opening continues with the hollow portion of the productportion, the hollow portion of the product portion is exposed on asurface of the product portion by removing the blowing opening. As aresult, molten metal might flow into the hollow portion of the sand moldfrom the vulnerable portion or hollow portion of the blowing opening.

The present invention provides a molding method of a sand mold usingfoamed sand, a molding die, and a sand mold, each of which restrainsmolten metal from flowing into the sand mold from a vulnerable portionor hollow portion of that blowing opening of the sand mold using thefoamed sand which is exposed on a surface of a product portion.

Aspect of Invention

The following aspects of the invention exemplify configurations of thepresent invention, and are described in an itemized manner in order tofacilitate the understanding of the various configurations of thepresent invention. Each item does not limit the technical scope of thepresent invention, and the technical scope of the present invention mayinclude configurations in which constituents of each item are partiallyreplaced, omitted, or supplemented by additional constituents whiletaking into consideration embodiments of the present invention.

A first aspect of the present invention relates to a molding method of asand mold including a hardened layer in a predetermined thickness rangefrom an outer layer part. The molding method of a sand mold including ahardened layer in a predetermined thickness range from an outer layerpart, includes: forming a cavity and a filling opening of a die so thata dimension b, which is a largest dimension between two intersections ofstraight lines passing through a section of a boundary portion betweenthe cavity and the filling opening of the die, with respect to anoutside line of the section, is less than a predetermined ratio withrespect to a thickness dimension d of that part of a product portion ofthe sand mold from which a blowing opening molded in the filling openingprojects, the product portion being formed by the cavity of the die; andfilling foamed sand into the cavity from the filling opening of the die.

According to the above aspect, the foamed sand filled into the cavityvia the filling opening of the die has a structure including a hardenedlayer within a predetermined thickness range from the outer layer partnot only in the cavity but also in the filling opening. That is, theproduct portion and the blowing opening of the sand mold are eachconstituted by the hardened layer, and a vulnerable portion or hollowportion. Further, the product portion and the blowing opening are eachconfigured such that a thickness of the vulnerable portion or hollowportion is generally one-third of a whole thickness of the productportion or the blowing opening, and a thickness of each hardened layercovering the vulnerable portion or hollow portion is generally one-thirdof the whole thickness. Although a boundary between the vulnerableportion and the hardened layer does not necessarily appear clearly, thethicknesses at the time when a minute range having a necessary strengthis assumed the hardened layer have the abovementioned values. Thepresent aspect focuses on a relationship between a dimension of theproduct portion of the sand mold and a dimension of the blowing openingthereof on molding the sand mold by use of the foamed sand.

More specifically, the present aspect focuses on a ratio between (i) thedimension b, which is a largest dimension between two intersections ofthe straight lines passing through the section of the boundary portionbetween the cavity and the filling opening of the die, with respect tothe outside line of the section, and (ii) the thickness dimension d ofthat part of the product portion of the sand mold from which the blowingopening molded in the filling opening projects, the product portionbeing formed by the cavity of the die. Then, the cavity and the fillingopening of the die are configured such that the dimension b is less thana predetermined ratio with respect to the dimension d. When the foamedsand is filled into the cavity from the filling opening of the die thusconfigured so as to perform molding, a sufficient thickness for thehardened layer in that part of the product portion from which theblowing opening is removed is secured. This inhibits molten metal fromflowing into the sand mold from the vulnerable portion or hollow portionof the blowing opening exposed on a surface of the product portion ofthe sand mold.

In the above aspect, values of b and d may be set so as to satisfyb<d/2. In the present aspect, a relationship of the values of thedimension b and the dimension d is set to b<d/2, and the foamed sand isfilled into the cavity from the filling opening of the die, so as toperform molding. In the dimensional relationship, the foamed sand isfilled into the cavity from the filling opening of the die, so as toperform molding. In a state where the blowing opening is removed fromthe product portion, a sufficient thickness is secured for the hardenedlayer of a part where the blowing opening is removed. This preventsmolten metal from flowing into the sand mold from the vulnerable portionor hollow portion of the blowing opening exposed to the surface of theproduct portion.

A second aspect of the present invention relates to a molding die formolding a sand mold including a hardened layer in a predeterminedthickness range from an outer layer part. The molding die includes acavity, and a filling opening communicating with the cavity andconfigured to fill the foamed sand into the cavity. The cavity and thefilling opening are configured such that a dimension b, which is alargest dimension between two intersections of straight lines passingthrough a section of a boundary portion between the cavity and thefilling opening, with respect to an outside line of the section, is lessthan a predetermined ratio with respect to a thickness dimension d ofthat part of a product portion of the sand mold from which a blowingopening molded in the filling opening projects, the product portionbeing formed by the cavity of the die.

In the above aspect, values of b and d may be set so as to satisfyb<d/2.

A third aspect of the present invention relates to a sand mold molded byfilling foamed sand into a cavity from a filling opening of a die sothat the sand mold includes a hardened layer in a predeterminedthickness range from an outer layer part. The sand mold includes: aproduct portion molded in the cavity of the die, and a blowing openingmolded in the filling opening. A dimension b, which is a largestdimension between two intersections of straight lines passing through asection of a boundary portion between the product portion and theblowing opening, with respect to an outside line of the section is lessthan a predetermined ratio with respect to a thickness dimension d ofthat part of the product portion from which the blowing openingprojects.

In the above aspect, values of b and d may be set so as to satisfyb<d/2.

When the molding die according to the second aspect is used in themolding method of the sand mold according to the first aspect, it ispossible to obtain the same effect as the effect of the molding methodof a sand mold according to the first aspect. Further, the sand moldaccording to the third aspect is obtainable by performing the moldingmethod of a sand mold according to the first aspect, or obtainable byperforming molding by use of the molding die according to the secondaspect. Note that when the sand mold according to the third aspect isused for casting, the blowing opening is removed.

Since the first to third aspects of the present invention are configuredas such, it is possible to restrain molten metal from flowing into thesand mold from the vulnerable portion or hollow portion of that blowingopening of the sand mold using the foamed sand which is exposed on thesurface of the product portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the invention will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1A is a schematic sectional view of a sand mold molded by a moldingmethod of a sand mold using foamed sand according to an embodiment ofthe present invention, and illustrates a dimensional relationshipbetween a blowing opening and a product portion of the sand mold,according to the embodiment of the present invention;

FIG. 1B illustrates a dimensional relationship between a blowing openingand a product portion of a sand mold, according to a comparativeexample;

FIG. 2A is a schematic sectional view of a die and a sand-mold moldingdevice to which the embodiment of the present invention is applicable,and illustrates an example in which the embodiment is applied to ahorizontally split type;

FIG. 2B is a schematic sectional view of a die and a sand-mold moldingdevice to which the embodiment of the present invention is applicable,and illustrates an example in which the embodiment is applied to avertically split type; and

FIG. 3 is a sectional view diagrammatically illustrating an overallconfiguration of a sand-mold molding device of a related art that isapplicable to the embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The following describes a mode for carrying out the present inventionwith reference to the accompanying drawings. Note that, in thisdescription, the same part as a constituent in a related art or anequivalent part to the constituent in the related art is indicated bythe same sign as the constituent in the related art, and detailedexplanations thereof are omitted. A molding method of a sand mold usingfoamed sand according to the embodiment of the present invention is suchthat a die 2 is set in a sand tank 12, and foamed sand S in the sandtank 12 is pressurized by a pressurization mechanism 13, as illustratedin FIG. 3. Hereby, the foamed sand S is filled into a cavity C of thedie 2 via a filling opening 5. The die 2 is heated to around 150° C. to300° C., so as to vaporize water in the foamed sand S filled in thecavity C, thereby solidifying the foamed sand S. After that, the die 2is opened and a sand core thus molded is taken out therefrom, and thus,a sand mold 20 illustrated in FIG. 1A is molded.

The sand mold 20 includes a product portion 22 molded inside the cavityC of the die 2, and a blowing opening 24 formed inside the fillingopening 5. Here, the sand mold 20 is illustrated in FIG. 1A such thatonly an area where the blowing opening 24 projects is extracted out ofthe product portion 22 having a more complicated shape as a whole, so asto show its sectional view. In predetermined thickness ranges fromrespective outer layer parts of the product portion 22 and the blowingopening 24, hardened layers 22H, 24H are formed. Further, vulnerableportions or hollow portions 22S, 24S are formed inside the hardenedlayers 22H, 24H. In a process of heating and hardening of the foamedsand S, water glass and an aggregate are accumulated in an outer layerpart of a molded product, so that a minute hardened layer having anecessary strength is formed in a predetermined thickness range from theouter layer part of the molded product. Due to this mechanism, theproduct portion 22 and the blowing opening 24 are each configured suchthat a thickness of the vulnerable portion or hollow portion 22S, 24S isgenerally one-third of a whole thickness of the product portion 22 orthe blowing opening 24. Further, each of the hardened layers 22H, 24Hcovering the vulnerable portion or hollow portion 22S, 24S has athickness of generally one-third of the whole thickness of the productportion 22 or the blowing opening 24.

In the embodiment of the present invention, b indicates a dimension fora largest distance between intersections of straight lines passingthrough a section of a boundary portion between the product portion 22and the blowing opening 24, with respect to an outside line of thesection, as illustrated in FIG. 1. The molding is performed so that thedimension b is less than a predetermined ratio with respect to athickness dimension d of that part of the product portion 22 from whichthe blowing opening 24 projects. More specifically, values of b and dare set so that b<d/2 is satisfied.

A specific method of setting ranges of the values of b and d is asfollows. As described above, in the sand mold 20 molded by the presentmethod, the thickness of the vulnerable portion or hollow portion 24S isgenerally ⅓b with respect to the whole thickness b of the blowingopening 24, and the thickness of the hardened layer 24H covering thevulnerable portion or hollow portion 24S is generally ⅓b. Further, thethickness of the vulnerable portion or hollow portion 22S is generally⅓d with respect to the thickness dimension d of that part of the productportion 22 from which the blowing opening 24 projects, and the thicknessof the hardened layer 22H covering the vulnerable portion or hollowportion 22S is generally ⅓d. In the product portion 22, in order tosecure a sufficient thickness for the vulnerable portion or hollowportion 22S of the product portion 22 not to be exposed in that part ofthe hardened layer 22H from which the blowing opening 24 is removed, thefollowing relationship should be satisfied. That is, as illustrated inFIG. 1A, a sum ⅔b of the thickness ⅓b of the vulnerable portion orhollow portion 24S of the blowing opening 24 and the thickness ⅓b of thehardened layer 24H should be less than the thickness ⅓d of the hardenedlayer 22H of that part of the product portion 22 in which the blowingopening 24 is formed. When the above dimensional relationship isdescribed briefly, it can be expressed as ⅔b<⅓d, namely, b<d/2.

Further, the die 2 used to obtain the sand mold 20 in the presentembodiment also has the same relationship as the dimensionalrelationship of the sand mold 20 illustrated in FIG. 1A. That is, thecavity C and the filling opening 5 of the die 2 are configured such thata dimension b, which is a largest dimension between two intersections ofstraight lines passing through a section of a boundary portion betweenthe cavity C and the filling opening 5 (see FIG. 3), with respect to anoutside line of the section, is not more than a predetermined ratio withrespect to a dimension of a thickness d of that part of the sand mold 20formed by the cavity C of the die 2 from which the blowing opening 24projects. That is, the cavity C and the filling opening 5 of the die 2are configured such that values of b and d satisfy b<d/2. Thus, the sandmold 20 illustrated in FIG. 1A can be obtained by molding a sand mold byuse of the die 2 configured as such.

Note that the embodiment of the present invention is applicableregardless of the placement of a parting line of the die 2 to be usedfor molding of the sand mold 20. For example, the embodiment isapplicable to a horizontally split type 2V in which a parting line PLextends laterally as illustrated in FIG. 2A, and to a vertically splittype 2H in which a parting line PL extends in an up-down direction asillustrated in FIG. 2B. In FIGS. 2A, 2B, a reference sign 15 indicates apress fitting plate, and a reference sign 15 a indicates a press fittingopening. Here, in a case where the embodiment is applied to thehorizontally split type 2V, the filling opening 5 generally has acircular-cone shape, and a sectional shape of a boundary portion of thefilling opening 5 with respect to the cavity C is circular. In view ofthis, the dimension b between two intersections of straight linespassing through the section of the boundary portion of the fillingopening 5 with respect to the cavity C, and an outside line of thesection is uniform and largest in any direction, in general.

On the other hand, in a case where the embodiment is applied to thevertically split type 2H, the filling opening 5 may be provided only onone die, and a sectional shape of a boundary portion of the fillingopening 5 with respect to the cavity C may be asymmetric (for example,semicircular). In such a case, the sectional shape of the boundaryportion of the filling opening 5 with respect to the cavity C may beasymmetric. Accordingly, the dimension b between two intersections ofstraight lines passing through the section of the boundary portion ofthe filling opening 5 with respect to the cavity C, and an outside lineof the section varies depending on a direction where the straight linespassing through the section extend. In this case, the dimension b is setto a largest dimension between the two intersections of the straightlines passing through the section and the outside line of the section.

According to the embodiment of the present invention, the cavity C andthe filling opening 5 of the die 2 are configured such that thedimension b, which is the largest dimension between two intersections ofthe straight lines passing through the section of the boundary portionbetween the cavity C and the filling opening 5 of the die 2, withrespect to the outside line of the section, and the thickness dimensiond of that part of the product portion 22 formed by the cavity C of thedie 2 from which the blowing opening 24 projects satisfy b<d/2. Then,the foamed sand S is filled into the cavity C from the filling opening 5of the die 2 configured as described in FIG. 3, so as to mold the sandmold 20. Hereby, the hardened layer 22H having a sufficient thickness issecured in that part of the product portion 22 from which the blowingopening 24 is removed. Accordingly, it is possible to inhibit moltenmetal from flowing into the vulnerable portion or hollow portion 22S ofthe product portion 22 at the time of casting.

Note that FIG. 1B illustrates a dimensional relationship between ablowing opening 24 and a product portion 22 of a sand mold 20′,according to a comparative example relative to the embodiment of thepresent invention. In the comparative example, a sum ⅔b of a thickness⅓b of a vulnerable portion or hollow portion 24S of the blowing opening24 and a thickness ⅓b of a hardened layer 24H is set to not less than athickness ⅓d of a hardened layer 22H of the product portion 22. When theabove dimensional relationship is described briefly, it can be expressedas ⅔b≥⅓d, namely, b≥d/2. In a case of the comparative example of FIG.1B, the hardened layer 22H is not secured in that part of the productportion 22 from which the blowing opening 24 is removed, therebyresulting in that the vulnerable portion or hollow portion 22S isexposed. It can be understood that, according to the comparativeexample, it is difficult to inhibit molten metal from flowing into thevulnerable portion or hollow portion 22S of the product portion 22 atthe time of casting.

What is claimed is:
 1. A molding die for molding a sand mold including ahardened layer in a predetermined thickness range from an outer layerpart, the molding die comprising: a cavity; and a filling openingcommunicating with the cavity and configured to fill the foamed sandinto the cavity, wherein: the cavity and the filling opening areconfigured such that a dimension b, which is a largest dimension betweentwo intersections of straight lines passing through a section of aboundary portion between the cavity and the filling opening, withrespect to an outside line of the section, is less than a predeterminedratio with respect to a thickness dimension d of a part of a productportion of the sand mold from which a blowing opening molded in thefilling opening projects, the product portion being formed by the cavityof the die, and a thickness of a vulnerable portion or hollow portion isgenerally ⅓b with respect to the whole thickness b of the blowingopening, a thickness of the hardened layer covering the vulnerableportion or hollow portion is generally ⅓b, a thickness of the hardenedlayer of the product portion is generally ⅓d, and a sum ⅔b of thethickness ⅓b of the vulnerable portion or hollow portion of the blowingopening and the thickness ⅓b of the hardened layer is less than athickness ⅓d of the hardened layer of a part of the product portion inwhich the blowing opening is formed.
 2. The molding die according toclaim 1, wherein: values of b and d are set so as to satisfy b<d/2.